Great tubes. I believe, these are as good as any other butyl tubes out there. I've been using these for several years. They are light and no more prone to flats than heavier tubes. I also like the unthreaded valves.
I have not ridden on these tubes very long. They have not put me on the road side with a wheel and tire off cursing at the tube. I did have the opportunity to give a tube to a stranded rider and she recognized the tube and liked them.
These seem to be very high quality tubes. The rubber in the tube is very uniform in thickness and when inflated outside the tire there is no ballooning in one area and constrictions in others. I have had however, problems getting them mounted and not having pinch flats. The pinch flat always seemed to be at the base of the valve. I finally realized that the reenforced area at the base of the valve doesn't like to bend very easily and let the tube slide past the tire bead and seat inside the tire. These tubes also don't seem to have as much powder on them as many other tubes do and because of this they hang up on the tire pretty easily. Recently I started using Ru-Glide, which is the mounting fluid used on car wheels and tires, when I replace a tube. This seems to have fixed that problem by allowing the tire and tube to slide by each other. Ru-Glide can be bought at auto parts stores. I highly recommend the tube.
I have tried other tubes, but this one works well for me and it is light. I think I am rolling much easier (gained .5 miles on my average) and the best part is that it hold the air pressure longer than any other tubes.